1. Technical Field of the Invention
The present invention relates to fuel injection apparatuses or systems for injecting fuel into cylinders of internal combustion engines and methods of manufacturing the same.
2. Description of the Related Art
An existing fuel injection apparatus for a diesel engine includes an accumulator, a plurality of injectors, a fuel supply unit, and a controller. (Such an apparatus is disclosed, for example, in Japanese Patent First Publication No. 2001-82230.)
The accumulator is provided to store therein high-pressure fuel.
Each of the injectors is connected to the accumulator and works to inject the high-pressure fuel in the accumulator into one of a plurality of cylinders of the diesel engine.
The fuel supply unit works to supply the high-pressure fuel to the accumulator. The fuel supply unit includes a low-pressure pump connected to a fuel tank, a high-pressure pump connected to the accumulator, and a solenoid-controlled valve connected between the low-pressure and high-pressure pumps.
The low-pressure pump works to provide fuel from the fuel tank to the high-pressure pump. The high-pressure pump works to pressurize the fuel from the low-pressure pump to obtain the high-pressure fuel and provide the high-pressure fuel to the accumulator. The solenoid-controlled valve works to change, when supplied with electric current, the rate of fuel flow from the low-pressure pump to the high-pressure pump. In addition, the fuel leakages from the fuel supply unit and the injectors are configured to be returned to the fuel tank.
The controller works to control the fuel supply rate of the fuel supply unit (i.e., the rate of fuel flow from the low-pressure pump to the high-pressure pump) through manipulation of the electric current supplied to the solenoid-controlled valve. Specifically, the controller is configured to:
determine a target fuel supply rate of the fuel supply unit based on a target fuel pressure in the accumulator,
determine a base target value of the electric current supplied to the solenoid-controlled valve as a first function of the target fuel supply rate,
determine a correction value as a second function of the target fuel supply rate,
correct the base target value of the electric current using the correction value to obtain a final target value of the electric current, and
manipulate the electric current supplied to the solenoid-controlled valve to have the final target value, thereby bringing the fuel supply rate of the fuel supply unit into agreement with the target fuel supply rate.
The above configuration of the controller is derived from the following considerations.
In general, the fuel injection apparatus is manufactured as a member of a fuel injection apparatus group in mass production. Due to manufacturing tolerances, there exist slight differences in characteristics among the fuel supply units of different members of the group.
Accordingly, the first function is so defined to be used for all members of the fuel injection apparatus group, and the second function is individually defined for each member of the group to achieve accurate fuel supply rate control.
According to a conventional approach, the second function is defined by the controller during operation of the diesel engine at a specific condition (e.g., an idling condition).
However, as to be described hereinbelow, it is difficult for the controller to accurately define the second function during operation of the diesel engine.
FIG. 4 shows the relation between the electric current supplied to the Solenoid-Controlled Valve (to be referred to as SCV current hereinafter) and the fuel supply rate of the fuel supply unit.
The controller has a map stored therein, which represents the first function between the target fuel supply rate of the fuel supply unit and the base target value of the SCV current; the first function can also be represented by the line a-a in FIG. 4.
At an idling condition of the diesel engine, the controller first determines the base target fuel supply rate Q1, and then determines the base target value i1 of the SCV current by means of the map, as indicated by the point A in FIG. 4.
Further, the controller determines the actual value i2 of the SCV current, and then defines the second function as (i2−i1). In other words, the controller determines that the actual flow characteristics of the fuel supply unit are as indicated by the line b-b in FIG. 4.
The above definition of the second function is based on the assumption that the actual fuel supply rate of the fuel supply unit at the idling condition of the diesel engine is equal to the base target fuel supply rate Q1, as indicated by the point B in FIG. 4. However, when there is an excessive amount of the fuel leakages from the fuel supply unit and the injectors, the actual fuel supply rate Q2 may be greater than the target fuel supply rate Q1, as indicated by the point C in FIG. 4. In this case, the actual flow characteristics of the fuel supply unit are, in fact, as indicated by the line c-c in FIG. 4.
Since the actual fuel supply rate Q2 of the fuel supply unit is generally unknown to the controller during operation of the diesel engine, it is difficult for the controller to properly define the second function. Accordingly, it is difficult for the controller to accurately correct the base target value of the SCV current to secure the accuracy of the final target value of the same.
Consequently, the controller cannot bring the actual fuel supply rate of the fuel supply unit into agreement with the target fuel supply rate, and thus cannot accurately and quickly control the fuel pressure in the accumulator.